1. Field of the Invention
Carbonaceous fuels, such as coal, containing appreciable amounts of sulfur and nitrogen are generally prohibited from widespread use because combustion of these fuels directly or gasification followed by combustion produces unacceptable levels of nitrogen and sulfur oxides. Attempts to reduce the formation of sulfur and nitrogen oxides by admixing with substances such as lime prior to combustion only gives rise to new problems such as increased residue disposal, critical need for homogenity of the admixture and cost. This invention relates to the treatment of fuel gases to substantially remove sulfur compounds and to decompose ammonia by contacting the fuel gas with zinc oxide at elevated temperatures.
2. Description of the Prior Art
Gasification of carbonaceous fuel followed by treatment of the produced fuel gas with a number of chemically reactive and/or absorptive scrubbers have been used in the past. Sulfur compounds such as H.sub.2 S can be removed using a number of prior processes such as aqueous alkali-carbonate processes, aqueous alkanolamine systems and physical absorption processes. Nitrogen compounds which lead to nitrogen oxide formation during combustion, principally ammonia (NH.sub.3), can be removed simply by quenching the gases to temperatures below 150.degree. F. using water. However, incorporation of these processes reduces the sensible heat of the fuel gas and results in a thermally less efficient process. The only process known to the applicants for the decomposition of ammonia in the presence of H.sub.2 S at elevated temperatures uses iron catalysts as taught by Akio Kazusaka and Isamu Toyoshima, Promoter Action of Potassium Oxide in Ammonia Synthetic Iron Catalyst, J. Rest. Inst. Catal., 21 (2), 150-6 (1973).
Removal of oxides of sulfur and nitrogen as a mixture of compounds makes the recovery of these chemicals for their commercial value difficult because additional process steps must be introduced to effect separation of the individual oxides.
It is readily appreciated that a method for the simultaneous removal of sulfur and nitrogen components of a fuel gas stream without requiring a decrease in the temperature of the fuel gas stream will result in efficient use of high sulfur and nitrogen containing carbonaceous fuels, such as coal.